The titular antagonist known only as the Ink Thief steals the power of imagination by sucking the "ink" out of books and drawings. At the start of the show, brother and sister Jim and Sam stumble upon his gothic world filled with Oobs, Bumps, and other imaginary creatures. During the course of the show, the children's friendship is tested as Jim gets seduced by the Ink Thief, whereas Sam fights to stop him. Each episode is peppered with plot-specific songs, giving the show a musical feel.